Upon performing data communications, a transmitting device typically scrambles a bit block constituted of data to be transmitted into a scrambling sequence, modulates the same, and transmits, to a receiving device, the modulated signal together with a reference signal for demodulation (demodulation reference signal (DM RS)). In this case, the receiving device estimates a channel through the DM RS of the received signal and uses the estimated channel for demodulating the received signal.
The data bit block obtained after demodulation is descrambled using the same scrambling sequence as that used in the transmitting device. Scrambling and descrambling are provided to randomize the influence of interference signals on the data bit block. For signal demodulation and scrambling using the DM RS, here, the transmitting device and the receiving device should share the information necessary for generating the same DM RS and scrambling sequence. To that end, typical cellular communication systems allow the broadcast signal transmitting a DM RS to provide a user equipment (UE) (that is a terminal or a device) in the cell with parameters necessary for generating the DM RS and/or scrambling sequence, so that the UEs may exactly receive the DM RS from the broadcast signal based on the parameters.
The 3rd Generation Partnership Project (3GPP), an organization for standardizing asynchronous cellular mobile communications, discusses the idea for allowing a long term evolution (LTE) standard, a next-generation mobile communication system, to support wireless communications between UEs or between devices, so-called device-to-device (D2D) communication, as well as wireless communications between a base station (BS) to a UE. The conventional LTE standard is only supportive of the wireless communication between a BS to a UE, and the generation of DM RSs and scrambling have been done in a way appropriate for such communication environment.
In the conventional LTE wireless communication environment, it is the base station and the terminal in the service coverage of the base station which perform data communication, and the base station and the terminal may easily share the information necessary for generating DM RSs and initializing a scrambling sequence. However, D2D communications may encounter situations where the terminals or devices participating in data communication may belong to the service coverage of different base stations, a specific terminal or device cannot be served by a base station or departs from the service coverage, rendering it difficult for devices to share the information necessary for generating DM RSs and initializing a scrambling sequence. Among others, support of one-to-many communications, i.e., broadcast communications, between devices in the 3GPP LTE standard, is a main topic of the ongoing discussion.
Further, the 3GPP discusses backing up the operation for a D2D terminal to discover other neighboring D2D terminals in the LTE standard. For this purpose, each D2D terminal transmits a discovery signal. The discovery signal is used for other D2D terminals to recognize the presence of the D2D terminal Each D2D terminal transmits its own discovery signal within some of time and frequency resources configured for communicating the discovery signal and attempts to detect the discovery signals transmitted from other D2D terminals using the remainder of the time and frequency resources. Thereafter, the D2D terminals determine whether there are D2D terminals corresponding to the time and frequency resources where the detection has been attempted. The discovery signal may include a message containing information relating to the terminal that has transmitted the discovery signal and a DM RS for demodulating the message. The bits constituting the message block may be scrambled before modulated.
The above-described D2D discovery operation should be supported to allow for discovery between D2D terminals in the service coverage of different base stations and D2D discovery between a radio resource control (RRC) connected terminal and an RRC idle terminal.
Existing DM RSs and preamble generation schemes defined in the LTE standard cannot apply to D2D communications. For example, in a case where D2D terminals belong to the service coverage of different base stations, generation of a DM RS sequence requires an inter-base station signaling overhead for sharing the information regarding the base stations which the D2D terminals respectively belong to. Further, unless the D2D terminals can be served by the base stations, they cannot utilize base station-related information and higher signaling from the base stations that are inevitable for generating DM RSs and preambles.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.